Phase coder alignment system



S. ZADOFF PHASE CODER ALIGNMENT SYSTEM June 18, 1963 5 Sheets-Sheet 1Filed April 24, 1957 i l l l l l i l MULTIPLE ADVANCE 4 EH W EH Em Em aMW TL mw Wm. W m. fl Q 7 L a 0 OSCILLATOR atc 3,094,696 Patented June18, 1963 dice $994,696 PHASE (IQDER ALHGNMENT SYSTEM Solomon Zadofi,Flushing, NFL, assignc-r to Sperry Rand Corporation, a corporation orDelaware Filled Apr. 24, 1957, Set. No. 654,969 16 Claims. (El. 343-103)This invention relates to communication systems utilizing phase codedpulsed carrier signals and, more particularly, to signal receiving meansfor use in such systems for aligning locally generaited phase codedsignals with the transmitted phase coded pulsed carrier signals.

In co-pending patentwapplication Serial No. 588,570, filed on May 31,1956, in the names of Robert L. Frank and Solomon Zadotf and assigned tothe present assignee, there is disclosed a phase coded hyperbolicnavigation system utilizing phase coded pulsed carrier transmissions.Phase coding is defined therein as he introduction of discrete amountsof phase shift the carrier of a pulsed signal, the phase shift beingintroduced during the time interval between the occurrence of theindividual pulses. In co-pending patent application Serial No. 650,5 34,filed on April 3, 1957, in the name of Robert L. Frank, it is shown thatdefinite systemic advantages accrue if the aforementioned phase shiftsfollow certain predetermined progressions. For example, by theutilization of particular phase codes providing for such predeterminedprogressions, the problem of distinguishing between a desired phasecoded signal and other signals is simplified to a considerable degree.

Another advantage attributable to the technique of phase coding, whichis recognized by the present invention, is that a locally generatedphase coded signal may be readily phase synchronized with a transmittedphase coded signal, certain of whose characteristics are known inadvance.

It is the general object of the present invention to provide means forsynchronizing a locally generated phase coded signal with a receivedphase coded signal having predetermined phase characteristics.

Another object of the present invention is to crosscorrelate a locallygenerated phase coded signal with a received phase coded signal so as togenerate a control signal for use in phase aligning the locallygenerated phase coded signal with the received phase coded signal.

1 m additional object is to cross-correlate a locally generated phasecoded signal with a received phase coded signal to produce a controlsignal for modifying the time of occurrence of the locally generatedsignal for purposes of aligning the locally generated signal with thereceived signal.

A further object of the present invention is to mix a locally generatedphase coded signal with a received phase coded signal so as to producepredetermined beat frequencies the presence of which is indicative ofmisalignment between the locally generated signal and the receivedsignal.

Yet another object is to compare in phase a locally generated phasecoded signal with a received phase coded signal so as to generate anerr-or signal Whose frequency is indicative of the rate of change ofphase misalign men-t between the locally generated signal and thereceived signal.

These and other objects of the present invention, as will appear as thespecification proceeds, are accomplished by the provision of phasedetection apparatus adapted to receive a phase coded signal and alocally generated phase coded signal, each signal being definable by thesame matrix describing the phase progression of the coded signal asmemured relative to the phase of an arbitrary continuous Wave signal.There is produced at the output of the phase detection apparatus asignal having substantially only a DO component in the event that thelocally generated signal and the received signal are in phase alignment.On the other hand, there is produced at the output of the phasedetection apparatus a signal containing certain predetermined lowfrequency components in the event of misalignment between the locallygenerated signal and the received signal.

The matrices defining both the received and the 10- cally generatedphase coded signals are comprised of a predetermined number of rows andthe same number of columns. The aforementioned output signal from thephase detection apparatus substantially contains only a DC. componentwhen both the rows and the columns of the respective matrices definingthe locally generated signal and the received signal are in alignment.Said output signal contains predictable components whose frequcncies aredetermined by the number of rows of misalignment between the locallygenerated and received signal matrices in the event that the columns arein alignment.

According to the present invention, a plurality of narrow band passfilters, connected to the output of the phase detection apparatus, aretuned to pass the aforementioned signal components. The individualoutputs of the band pass filters are summed together so that a resultantsignal is produced whose presence is indicative of the condition ofcolumn alignment but row misalignment of the matrices defining thelocally generated signal and the received signal. The resultant signalis then applied to the source which produced the locally generated phasecoded signal to vary the time of occurrence of the locally generatedsignal, relative to the time of occurrence of the received signal aslong as the afore mentioned resultant signal persists. Upon the completerow and column alignment of the matrices defining the received andlocally generated phase coded signals, said resultant signal disappearsand the time shifting of the locally generated phase coded signal isterminated.

The resultant signal derived from the outputs of the band pass filterappears only in the event of column alignment between the aforementionedmatrices. In order to achieve column alignment between the matrixdefining the received signal and the matrix defining the locallygeneriated signal in the general case of time misalignment therebetween,means are provided to drift the locally generated matrix of signalsrelative to the matrix of received signals and to stop said drift assoon as the aforementioned resultant signal appears.

Additionally, means are provided to positively identify the conditionwherein the matrices defining the received and locally generated phasecoded signals are in both row and column alignment.

For a more complete understanding of the present invention, referenceshould be had to the following description and to the appended drawingsof which:

FIG. 1 is a block diagram of a suitable transmitter of phase codedpulsed carrier signals to which the phase coder alignment apparatus ofthe present invention is responsive;

FIG. 2 is a series of matrices and tables useful in explaining theoperation of the present invention;

FIG. 3 is a block diagram of a receiver embodying the phase coderalignment apparatus of the present invention Which is adapted to receivethe signals transmitted by the apparatus of FIG. 1;

FIG. 4 is a schematic diagram of the actuating mechanism for the phasecoder used in FIG. 3; and

FIG. 5 is a series of waveforms of some of the signals that are producedwithin the structure of FIG. 3.

In FIG. 1, a source of continuous Wave carrier signal is generallyrepresented by oscillator 1. The output of oscillator 1 is applied vialine to the signal input of phase coder 2, the control input to which isderived from the output of pulse source 3 via line 4. Pulse source 3represents generally a source of continuous pulses of fixed repetitionrate. Phase coder 2 comprises, in the illustrative case of FIG. 1, amechanical stepping switch 6 whose movable arm 7 advances one contactposition in response to individual pulses which are applied via line 4to stepping relay 8. Phase shifters 9, 1t 11, and 12 each have an inputconnected to a respective contact of stepping switch 6; the outputsthereof are connected together and are applied via line 13 to the signalinput are produced for one cycle of operation of the phase coder, itwill be seen that sixty-four switch contacts and associated phaseshifters are required. The extension of phase coder 2 to produce suchother phase codes is suggested by the dashed connections.

It will be seen that the signal appearing on line 13 is of the samefrequency as the signal input on line 5 but will bear a phaserelationship with respect thereto as determined by the particular phaseshifter with which movable arm 7 of stepping switch 6 is momentarily incontact. Phase shifters 9, 119, 11, and 12 are adjusted to producepredetermined amounts of phase shift so that the phase of the successiveoutput signals on line 13, as measured relative to the phase of theinput signal on line 5,. may be represented by a predetermined matrixsuch as matrix A of FIG. 2.

The individual terms or numerals of matrix A represent the multiplyingcoeflicients of a basic phase angle which may have a value, for example,of 135. Thus, matrix A is interpreted as having eight rows and eightcolumns of a total of sixty-four signals, each signal of which has aphase, as measured relative to an arbitrary continuous wave signal,which is equal to the product of 135, and a respective matrix numeral.For example, the first row of matrix A represents eight successivesignals each of Whose relative phase is successively 135 (l l35), 270 (2l35), 405 (3 l35) and so on.

As more fully disclosed in the aforementioned application Serial No.650,534, certain systemic advantages accrue when the sequential phaseprogression of the phase coded signal is adjusted to occur in apredetermined order. An example of such predetermined order is given bymatrix A.

Returning to FIG. 1 and as previously mentioned, the phase coded signaloutput of phase coder 2 is applied via line 13 to the signal input ofR-F amplifier 14. R-F amplifier 14 is adapted to pulse modulate thephase coded carrier signals applied thereto in response to modulatingpulses as derived from modulator 15. Modulator 15, in turn, is triggeredby pulses derived from pulse source 3 via pulse delay device 16. Delay16 produces a time differential between the operation of phase coder 2and the operation of R-F amplifier 14 to provide for the diminution oftransients, produced by the operation of phase coder 2, before the phasecoded pulsed carrier signals are passed by amplifier 14 for radiation byantenna 17.

The phase coder alignment apparatus of the present invention is embodiedin the receiver structure of FIG. 3. In FIG. 3, the phase coded pulsedcarrier signals, as may be transmitted by the structure of FIG. 1, arereceived by antenna 18 and amplified by R-F amplifier 19. The output ofamplifier 19 is applied to a first input of phase detector 20, areference signal input to which is derived from phase coder 21 via line22. Phase coder 21 may be of a form similar to that of illustrativephase coder 2 of FIG. 1 so as to produce phase coded signals defined bythe same matrix as the matrix describing the phase coded signalsproduced at output line 13 of phase coder 2.

Phase coder 21 structurally differs from phase coder 2. of FIG. 1 onlywith respect to its actuating mechanism. As previously discussed,movable arm 7 of phase coder 2 advances one contact position in responseto individual actuating pulses applied via line 4 to stepping relay 8.For purposes of the present invention, as will more fully be explainedhereinafter, the actuating mechanism of phase coder 21 is adapted notonly to advance its movable arm one contact position in response toindividual applied pulses, but also to abruptly advance the movable armby a predetermined plurality of contact positions in response to acontrol signal.

There is shown in FIG. 4 an illustrative simplified embodiment of theactuating mechanism of phase coder 21. Stepping relay 47 is adapted toreceive energizing pulses as applied via line 28 and is operative inresponse thereto, by means of linkage 511, operating arm 51, and pawl 52to rotate ratchet 53 through an angle occupied by one peripheral tooth.The angular motion of ratchet 53 is imparted via shaft 54 anddifferential 55 to gearing 56 which in turn advances movable arm 43 onecontact position in response to individual pulses applied via line 23.Gearing 56 is arranged to cause shaft 57 to rotate in equal an ularamounts with shaft 54 in the absence of any displacement of shaft 58,which is the second input to mechanical differential 55. Thus, theactuating mechanism so far described will operate in precisely the samefashion (in the absence of displacement of shaft 58) as does steppingswitch 6 of FIG. 1.

The additional solenoid and ratchet arrangement of FIG. 4 is adapted toproduce an abrupt displacement of movable arm 43 over a predeterminednumber of contact positions in response to actuation of solenoid 5? bymean of an essentially direct control voltage applied via line 27. Inresponse to said direct voltage, solenoid 59 is energized via acontinuous conductive path to ground including strip 611, affixed toshaft 61, which conductively connects contacts 62. Upon the energizationof solenoid 59", shaft 61 is abruptly displaced, opening contacts 152and rota-ting ratchet 63 through an angle occupied by a predeterminedplurality of circumferential teeth. Spring 69 returns shaft 61 to itslower or rest position against the resistance of dash pct 64 whichintroduces a fixed time delay between successive cycles of operation ofsolenoid '59 in the continued presence of the DC. control signal.

The rotation of ratchet 63 is imparted via shaft 58, differential 55,gearing 5d, and shaft 57 to movable arm 48. Movable arm 48 of FIG. 4corresponds to movable arm 7 of stepping switch 6 of FIG. 1. Althoughnot shown, it is assumed that each of the contacts 65 are connected torespective phase shift networks as is the case with the contacts ofstepping switch 6 of FIG. 1.

The carrier signal input of phase coder 21 of FIG. 3 is obtained fromvariable frequency oscillator 23 whose frequency is substantially thatof oscillator 1 of FIG. 1. The unitary advance input of phase coder 21is derived from the output of pulse generator 25 which nominallyoperates at the same repetition rate as that of pulse source 3 ofFIG. 1. The output of phase detector 211 is applied to the signal inputof sampling gate 29 which is rendered conductive by the pulses producedby generator 25 and applied via pulse delay 311.

As already mentioned, the phase coded signals transmitted by theapparatus of FIG. 1 are in the form of pulses. Assuming that thereceived signal and the reference inputs to phase detector 211 are intime alignment, the output signal therefrom is also in the form ofpulses. The purpose of delay 30 is to activate sampling gate 29 at atime slightly delayed relative to the start of the received pulses sothat the pulse envelopes produced at the output of phase detector 2!}are sampled by gate 29 during the leading edges thereof. The output ofsampling gate 29 is applied by conventional threshold circuit 26, lowpass filter 31 and DC. amplifier 70 to DC. meter 32.

It is shown in co-pending application Serial No. 650,- 534, that thereis produced at the output of phase detector 20 a signal having a DC.component in the sole event that the matrices defining the receivedsignal and reference signal in-puts thereto are in precise row andcolumn alignment. Such a condition of matrix alignment is represented bymatrices A and B of FIG. 2. Matrix A, for example, may represent thereceived signal input to phase detector 20 while matrix B represents thereference signal input thereto as applied via line 22, The rela H tivepositions of matrices A and B of FIG. 2 are arranged to indicate thatthe signals represented by corresponding matrix terms occur at the sametime at their respective inputs to phase detector 20.

The utility of the unique DC. signal component that is produced solelyin the event of precise row and column alignment between the matricesdefining the phase coded signal inputs to phase detector may bedemonstrated as follows. In certain types of communication systems forexample, in hyperbolic navigation systems, it is desirable to achievephase coherence between a remotely situated secondary timing standardand a highly precise locally situated primary standard. The primary andsec ondary timing standards may be respectively, a transmitter carrieroscillator and a receiver local oscillator. In such a case, coherence isachieved by communicating carrier oscillator phase information to thereceiver local oscillator.

The phase coding of the signals contemplated by the present inventionmay be considered to be a medium for the discriminatory reception by thereceiver of FIG. 3 of information representing the phase of the carriersignal generated by oscillator 1 of FIG. 1. The received carrier phaseinformation is employed in achieving phase coherence between oscillator23 of FIG. 3 and oscillator 1 of FIG. 1. The presence of a DC. signalcomponent at the output of detector 20 of FIG. 3 unambiguously signifiesthe attainment of coherence between the received phase coded signal andthe reference phase coded signal applied thereto. This, in turn,indicates that phase coherence has been established between oscillator23 of FIG. 3and oscillator 1 of FIG. 1.

A primary objective of the present invention is to rapidly accomplishphase coherence between the phase coded signals applied to detector 20of FIG. 3.

It will be recognized that in the geenral case the signals produced atthe output of phase coder 21 will not be initially in alignment with thereceived phase coded signals at the input of phase detector 20. Meansare therefore provided for varying the time of occurrence of the outputsignals of phase coder 21 to search for the received signals. Theaforementioned means include a source of drift bias 33 which is appliedvia conducting switch 34 to pulse generator to vary the frequency atwhich it i operating in a conventional manner. As the signal output ofphase coder 21 is drifted in time relative to the occurrence of thereceived phase coded signals, the columns of the reference matrix,representing the drifting signals, will ultimately occur at the sametime as the columns of the matrix describing the received signals. Uponthe event of such column alignment, the rows of the matrix Willgenerally be misaligned.

The present invention recognizes that in such a case of matrix columnalignment but row misalignment, one of a discrete number of lowfrequency signal components will be produced at the output of phasedetector 20.

Matrices C and D of FIG. 2 represent the aforementioned conditionwherein there is column alignment but row misalignment between thereceived and locally generated signal matrices. Inasmuch as the basicphase angle, of which the terms shown in the matrices are coefiicients,is the same for both matrices, the relative phase between the signalsrepresented by corresponding matrix terms may be ascertained by merelysubtracting corresponding terms. Assuming, for example, that matrix Crepresents the received signal at the input of phase detector 20 whilematrix D represents the locally generated signals at the reference inputthereto, Table E lists the individual phase differences betweencorresponding signals.

It was previously stated for illustrative purposes that the basic phaseangle, common to the received and locally generated phase codingmatrices, may be Referring to Table E, each numeral thereof must be mul-V tiplied by such basic phase angle, namely, 135. Table F lists thevalue of the cosine of the angle resulting from the multiplication ofthe individual terms of Table E with 135.

The significance of the cosine function is that phase detector 20produces an output signal whose amplitude is proportional to the cosineof the phase angle between the two input signals applied thereto as iswell known in the art. A pictorial representation of Table F is shown inwaveform A of FIG. 5. The vertical solid line portions of waveform Arepresent a plot of any one row of Table F, i.e., portion 37 has anamplitude of 0.707, portion 38 has an amplitude of +0.707, verticalportion 39 has an amplitude of 1, and so on. The Zero values of Table Fare shown as dots in waveform A. The time interval between thesuccessively plotted values of Table F in waveform A is made equal torepresent the equal time separation between the pulses at the sampledoutput of phase detector 20, which samples occur at equal timeintervals. The dotted line of waveform A is superimposed on the verticalsolid lines to denote the presence of a fundamental frequency, threecycles of which are produced each time a row of signal matrix C and arow of reference matrix D are simultaneously applied to their respectiveinputs of phase detector 20.

The pulsed signals appearing at the output of sampling gate 29 of FIG. 3thus contain the aforementioned low frequency component, which lowfrequency component is enhanced by pulse stretching filter 35. In otherwords, pulse stretching filter 35 operates on the solid line waveform Ato produce waveform B. Pulse stretching filter 35 may be of a form of alow pass filter to accomplish such result. The output of pulsestretching filter 35 is simultaneously applied to respective inputs ofband pass filters 37, 38, 39, and 40, each of which filters is tuned toa different harmonic of the basic low frequency signal which may appearat the output of pulse stretching filter 35.

In the case represented by matrices C and D of FIG. 2, wherein theapplied and reference signal matrices are aligned in column butmisaligned by one row, the third harmonic of the aforementioned lowfrequency signal is present at the output of pulse stretching filter 35.Band pass filter 39 is adapted to pass substantially only such frequencyto conventional threshold circuit 41, similar to threshold circuit 26.Circuits 26 and 41. each may be, for example, a back-biased diodeadapted to pass the signal output of filter 39 when it exceeds apredetermined amplitude.

Waveform C of FIG. 5 shows the signal present at the output of filter 39in the assumed case while waveform D is the signal derived therefrom andpassed by threshold circuit 41. The DC. component of waveform D ispassed by low pass filter 42 and applied to DC. amplifier 43. The outputof amplifier 43 is connected to the multiple advance control input ofphase coder 21 via line 27. Said output is also connected to a firstinput of summing circuit 45, a second input to which is derived from theoutput of -D.C. amplifier 70.

Switch 34 is normally closed thereby applying drift bias 33 to generator25. Upon the occurrence of an output signal from summing circuit 45,switch 34- is rendered nonconduotive and the drifting of generator 25ceases so as to restore the repetition rate of its pulses to therepetition rate of the received pulses of the phase coded signal. Thepresence of an output signal from either of the low pass filters 31 and42 is indicative of column alignment between the matrices defining thereceived signal and reference signal input-s to phase detector 20. Itshould be noted that an output signal from filter 31 signifies not onlycolumn alignment but row alignment as well.

In operation, assuming that the received signal and reference inputs ofphase detector 2% are as represented by matrices C and D of FIG. 2, thelow frequency signal represented by waveform C of FIG. will appear atthe output of 'filter 39. The DC. component of waveform C, whenexceeding a predetermined amplitude as fixed by the threshold circuit41, causes the abrupt advance of movable arm 48 of phase coder 21 by apredetermined number (N) of contact positions. In terms of matrix D ofFIG. 2, the abrupt advance of movable arm 48 by N contact positions willproduce a corresponding abrupt shift in matrix D, relative to matrix C,by one row, thereby aligning the matrices, inasmuch as there are Ncontact positions 65 of phase coder 21 for each row.

It has been ascertained that when the matrix defining the locallygenerated signal is in column alignment with the matrix defining thereceived signal but is misaligned therewith by other than one row,different harmonics of a low frequency f are present at the output ofphase detector 20, whose frequencies are related to the number of rowsof misalignment. More particularly, it has been observed that wherematrices such as C and D of FIG. 2 are misaligned by one row, theharmonic frequency of 3 is produced; when misaligned by two rows, theharmonic frequency of 2 is produced; when misaligned by three rows,

the base frequency of f is produced; and when misaligned by four rows,the harmonic frequency of 4 is produced.

'Additionally, it has been discovered that for seven rows ofmisalignment the same frequency is produced as results from one row ofmisalignment; six rows of misalignment produce the same frequency as tworows of misalignment and five rows of misalignment produce the samefrequency as three rows of misalignment. Thus, depending on the numberof rows of misalignment between the received and locally generatedsignal matrices, a frequency f or discrete harmonics thereof will beproduced.

Band pass filter 37 is tuned to pass the base frequency i; band passfilter 38 passes the harmonic frequency 2 band pass filter 3? passes theharmonic frequency 3 and band pass filter 40 passes the harmonicfrequency 4]". It should be observed that in the event that phase codedsignals represented by extended matrices are utilized, i.e., matricesincluding more than sixty-four phase coded signals, additional harmonicsof 1 will be produced.

As already discussed, frequency f and harmonics thereof are produced inthe event that the received and locally generated signal matrices are incolumn alignment but row misalignment. It readily will be appreciatedthat during the initial process of achieving that degree of matrixalignment, said matrices will in general be misaligned both in columnand in row. In the case of column misalignment of the matrices, thereare produced frequency components other than 1 and its harmonies. Suchother frequencies are intermediate 1 and its harmonics and for thatreason the illustrative embodiment of FIG. 3 utilizes band pass filtersto select only the proper predetermined frequency components.

The precise frequencies to which band pass filters 37, 38, 39, and 40are tuned may be determined in the following manner. By definition, theaforementioned basic phase angle of which the terms of the matrices arecoefficients is where p and N are integers greater than zero, and p isrelatively prime to N. That is, there are no integers a and b both ofwhich are less than N such that ap bN. As an example, if N equals 8,then Accordingly, p may have the values of l or 3 or 5, etc., any one ofwhich values will satisfy the requirement that p be relatively prime toN.

Thus, the phase angle of the general term of the reference signalmatrix, as applied via line 22 to phase detector 20, may be representedby where x and y respectively represent the row and column number of thegeneral term. The basic phase angle of the matrix defining the receivedsignal input to phase detector 20 may be represented by where Qrepresents the number of rows of misalignment between the signal andreference matrices. The phase difference between the individual terms ofthe signal and reference matrices may be ascertained by subtracting (1)from (2) to yield Now, let T equal the time interval between thesuccessive pulses comprising the rows of the matrices. The frequency ofthe difference angle, i.e., AS/T, can be shown to be equal to thefunction 21rpQ/NT. Accordingly, band pass filter 37 is tuned to pass thefrequency of Zn'P/NT; band pass filter 38 is tuned to pass the harmonicfrequency of 411-p/N T; band pass filter 39 is tuned to pass theharmonic frequency of 61rp/NT; and band pass filter 40 is tuned to passthe harmonic frequency of 81rp/NT.

It can be seen from the preceding description that the objects of thepresent invention have been achieved by the provision of phase coderalignment apparatus adapted to receive a phase coded pulsed carriersignal and to cross-correlate (as by means of a phase detector) saidreceived signal with a locally generated phase coded signal. Theinvention utilizes the unique properties of phase coded signals, whenused in a cross-correlating detection process, whereby discrete lowfrequency signal components are produced in the event that there iscolumn alignment between the reference and received signal matrices, butrow misalignment. The presence of such low frequency signals is detectedand a control signal is produced therefrom for abruptly adjusting thephase coder for the locally generated signal so as to quickly shift thelocally generated phase coded signal matrix relative to that of thereceived signal to produce phase alignment between the local signal andthe received signal matrices. The invention further provides forposifrom the true scope and spirit of the invention in its broaderaspects.

What is claimed is:

1. In combination, signal detector means having two inputs and an outputand adapted to receive at one of said inputs pulsed phase coded carriersignals defined by a predetermined matrix of N rows and N columns, alocal source for producing phase coded reference signals defined by saidmatrix, said local source including means for drifting said matrix ofreference signals in time relative to said matrix of carrier signals,means responsive to first and second control signals for deactivatingsaid means for drifting, and means for abruptly shifting said matrix ofreference signals in time relative to said matrix of carrier signals inincrements of matrix rows in response to said second control signal, theoutput of said local source being connected to the other of saiddetector inputs, said detector being operative to cross-correlate saidcarrier and reference signals so as to produce at said output a signalrelated to the relative phase therebetween, means for sampling theoutput signal of said detector in response to applied triggers, saidlocal source including a source of said triggers, means adapted toreceive the output signal of said sampling means for producing saidfirst control signal related to the DC. component thereof, and meansadapted to receive said output signal of said sampling means for sensingthe presence of harmonically related frequency components thereof andfor producing said second control signal in response thereto, means forapplying said first and second control signals to said means fordeactivating said means for drifting, and means for applying said secondcontrol signal to said means for abruptly shifting.

2. Apparatus as defined in claim 1 wherein said signal detector meanscomprises a phase detector.

3. Apparatus as defined in claim 1 wherein said means for producing saidfirst control signal comprises a low pass filter.

4. Apparatus as in claim 1 wherein said means for sensing comprises aplurality of band pass filters each tuned to a different harmonic of apredetermined frequency, the input terminals of said filters beingconnected to the output of said sampling means and the output ter minalsthereof being connected together.

5. Apparatus as defined in claim 4 wherein said predetermined frequencyis defined as being equal to 21rp/ N T where T represents the timeinterval between the successive pulses of said pulsed phase codedcarrier signal, and where p and N are integers greater than zero, pbeing relatively prime to N.

6. In combination, signal detector means having two inputs and an outputand adapted to receive at one of said inputs phase coded carrier signalsdefined by a predetermined matrix of N rows and N columns, a localsource for producing phase coded reference signals defined by saidmatrix, said local source including means for drifting said martix ofreference signals in time relative to said matrix of carrier signals,means responsive to the sum of first and second control signals fordeactivating said means for drifting, and means for abruptly shiftingsaid matrix of reference signals in time relative to said matrix ofcarrier signals in increments of matrix rows in response to said secondcontrol signal, the output of said local source being connected to theother of said detector inputs, said detector being operative to crosscorrelate said carrier and reference signals so as to produce at saidoutput a signal related to the relative phase therebetween, meansadapted to receive the output signal of said detector means forproducing said first control signal related to the DC. componentthereof, means adapted to receive said output signal of said detectormeans for sensing the presence of harmonically related frequencycomponents thereof and for producing said second control signal inresponse thereto, means for summing said first and second controlsignals and for apply- 10 ing the sum thereof to said means fordeactivating said means for drifting, and means for applying said secondcontrol signal to said means for abruptly shifting.

7. In combination, signal detector means having two inputs and an outputand adapted to receive at one of said inputs pulsed phase coded carriersignals defined by a predetermined matrix of N rows and N columns, alocal source for producing phase coded reference signals defined by saidmatrix, said local source including means for abruptly shifting saidmatrix of reference signals in time relative to said matrix of carriersignals in increments of matrix rows in response to a control signal,the output of said local source being connected to the other of saiddetector inputs, said detector being operative to cross-correlate saidcarrier and reference signals so as to produce at said output a signalrelated to he relative phase therebetween, means for sampling the outputsignal of said detector in response to applied triggers, said localsource including a source of said triggers, means adapted to receivesaid output signal of said sampling means for sensing the presence ofharmonically related frequency components thereof and for producing saidcontrol signal in response thereto, and means for applying said controlsignal to said means for abruptly shiftin 8. Apparatus as defined inclaim 7 wherein said signal detector means comprises a phase detector.

9. Apparatus as defined in claim 7 wherein said means for sensingcomprises a plurality of band pass filters each tuned to a differentharmonic of a predetermined frequency, the input terminals of saidfilters being connected to the output of said sampling means and theoutput terminals thereof being connected together.

10. Apparatus as defined in claim 9 wherein said predetermined frequencyis defined as being equal to 21rp/ NT where T represents the timeinterval between the successive pulses of said pulsed phase codedcarrier signal, and where p and N are integers greater than zero, 2being relatively prime to N.

11. In combination, signal detector means having two inputs and anoutput and adapted to receive at one of said inputs phase coded carriersignals defined by a predetermined matrix of N rows and N columns, alocal source for producing phase coded reference signals defined by saidmatrix, said local source including means for abruptly shifting saidmatrix of reference signals in time relative to said matrix of carriersignals in increments of matrix rows in response to a control signal,the output of said local source being connected to the other of saiddetector inputs, said detector being operative to cross-correlate saidcarrier and reference signals so as to produce at said output a signalrelated to the relative phase therebetween, means adapted to receivesaid output signal of said detector means for sensing the presence ofharmonically related frequency components thereof and for producing saidcontrol signal in response thereto, and means for applying said controlsignal to said means for abruptly shifting.

12. In combination, signal detector means having two inputs and anoutput and adapted to receive at one of said inputs pulsed phase codedcarrier signals defined by a predetermined matrix of N rows and Ncolumns, a local source for producing phase coded reference signalsdefined by said matrix, said local source including means for driftingsaid matrix of reference signals in time relative to said matrix ofcarrier signals, means responsive to first and second control signalsfor deactivating said means for drifting, and means for abruptlyshifting said matrix of reference signals in time relative to saidmatrix of carrier signals in increments of matrix rows in response tosaid second control signal, the output of said local source beingconnected to the other of said detector inputs, said detector beingoperative to crosscorrelate said carrier and reference signals so as toproduce at said output a signal related to the relative phasetherebetween, means for sampling the output signal of said detector inresponse to applied triggers, said local source including a source ofsaid triggers, means adapted to receive the output signal of saidsampling means for producing said first control signal related to theDC. component thereof, and means adapted to receive said output signalof said sampling means for sensing the presence of at least onecomponent thereof having a frequency of 21rpQ/NT and for producing saidsecond control signal in response thereto, where Q represents the numberof rows of misalignment between the matrices defining said carrier andreference signals, Where T represents the time interval betweensuccessive pulses of said pulsed phase coded carrier signal, and where pand N are integers greater than zero, p being relatively prime to N,means for applying said first and second control signals to said meansfor deactivating said means for drifting, and means for applying saidsecond control signal to said means for abruptly shifting.

13. In combination, signal detector means having two inputs and anoutput and adapted to receive at one of said inputs phase coded carriersignals defined by a predetermined matrix of N rows and N columns, alocal source for producing phase coded reference signals defined by saidmatrix, said local source including means for drifting said matrix ofreference signals in time relative to said matrix of carrier signals,means responsive to the sum of first and second control signals fordeactivating said means for drifting, and means for abruptly shiftingsaid matrix of reference signals in time relative to said matrix ofcarrier signals in increments of matrix rows in response to said secondcontrol signal, the output of said local source being connected to theother of said detector inputs, said detector being operative tocross-correlate said carrier and reference signals so as to produce atsaid output a signal related to the relative phase therebetween, meansadapted to receive the output signal of said detector means forproducing said first control signal related to the DC. componentthereof, means adapted to receive said output signal of said detectormeans for sensing the presence of at least one component thereof havinga frequency of 21rpQ/NT and for producing said second control signal inresponse thereto, where Q represents the number of rows of misalignmentbetween the matrices defining said carrier and reference signals, whereT represents the time interval between successive pulses of said pulsedphase coded carrier signal, and Where p and N are integers greater thanzero, 12 being relatively prime to N, means for summing said first andsecond control signals and for applying the sum thereof to said meansfor deactivating said means for drifting, and means for applying saidsecond control signal to said means for abruptly shifting.

14. In combination, signal detector means having, two inputs and anoutput and adapted to receive at one of said inputs pulsed phase codedcarrier signals defined by a predetermined matrix of N rows and Ncolumns, a local source for producing phase coded reference signalsdefined by said matrix, said local source including means for abruptlyshifting said matrix of reference signals in time relative to saidmatrix of carrier signals in increments of matrix rows in response to acontrol signal, the output of said local source being connected to theother of said detector inputs, said detector being operative tocross-correlate said carrier and reference signals so as .to produce atsaid output a signal related to the relative phase therebetween, meansfor sampling the output signal of said detector in response to appliedtriggers, said local source including a source of said triggers, meansadapted to receive said output signal of said sampling means for sensingthe presence of at least one component thereof having a frequency of21rpQ/NT where Q represents the number of rows of misalignment betweenthe matrices defining said carrier and reference signals, where Trepresents the time interval between successive pulses of said pulsedphase coded carrier signals, and where p and N are integers greater thanzero, p being relatively prime to N, and means for applying said controlsignal to said means for abruptly shifting.

15. In combination, signal detecting means having two inputs and anoutput and adapted to receive at one of said inputs phase coded carriersignals defined by a predetermined matrix of N rows and N columns, alocal source for producing phase coded reference signals defined by saidmatrix, said local source including controllable means for abruptlyshifting said matrix of reference signals in time relative to saidmatrix of carrier signals in increments of matrix rows, the output ofsaid local source being connected to the other of said detector inputs,said detector being operative to cross-correlate said carrier andreference signals so as to produce at said output a signal related tothe relative phase therebetween, and means adapted to receive saidoutput signal of said detector means for sensing the presence ofharmonically related frequency components thereof.

16. In combination, signal detecting means having two inputs and anoutput and adapted to receive at one of said inputs phase coded carriersignals defined by a predetermined matrix of N rows and N columns, alocal source for producing phase coded reference signals defined by saidmatrix, said local source including controllable means 'for abruptlyshifting said matrix of reference signals in time relative to saidmatrix of carrier signals in increments of matrix rows, the output ofsaid local source being connected to the other of said detector inputs,said detector being operative to cross-correlate said carrier andreference signals so as to produce at said output a signal related tothe relative phase therehetween, and means adapted to receive saidoutput signal of said detector means for sensing at least one componentthereof having a frequency of 21rpQ/N T where Q represents the number ofrows of misalignment between the matrices defining said carrier andreference signals, where T represents the time interval betweensuccessive pulses of said pulsed phase coded carrier signals, and wherep and N are integers greater than zero, p being relatively prime to N.

References Cited in the file of this patent UNITED STATES PATENTS

15. IN COMBINATION, SIGNAL DETECTING MEANS HAVING TWO INPUTS AND ANOUTPUT AND ADAPTED TO RECEIVE AT ONE OF SAID INPUTS PHASE CODED CARRIERSIGNALS DEFINED BY A PREDETERMINED MATRIX OF N ROWS AND N COLUMNS, ALOCAL SOURCE FOR PRODUCING PHASE CODED REFERENCE SIGNALS DEFINED BY SAIDMATRIX, SAID LOCAL SOURCE INCLUDING CONTROLLABLE MEANS FOR ABRUPTLYSHIFTING SAID MATRIX OF REFERENCE SIGNALS IN TIME RELATIVE TO SAIDMATRIX OF CARRIER SIGNALS IN INCREMENTS OF MATRIX ROWS, THE OUTPUT OFSAID LOCAL SOURCE BEING CONNECTED TO THE OTHER OF SAID DETECTOR INPUTS,SAID DETECTOR BEING OPERATIVE TO CROSS-CORRELATE SAID CARRIER ANDREFERENCE SIGNALS SO AS TO PRODUCE AT SAID OUTPUT A SIGNAL RELATED TOTHE RELATIVE PHASE THEREBETWEEN, AND MEANS ADAPTED TO RECEIVE SAIDOUTPUT SIGNAL OF SAID DETECTOR MEANS FOR SENSING THE PRESENCE OFHARMONICALLY RELATED FREQUENCY COMPONENTS THEREOF.